From the More pull down menu, select DNS Manager. You should be defaulted to your hosting plan's primary domain.

To view the zone file for an aliased domain click 'Change Zone' after 'Zone File Editor.' You should see a list of your aliased domains.

Find the domain you want to view the zone file for and click OK.

If you are trying to confirm nameservers for an aliased domain you recently added, scroll to the bottom of the zone file until you see the 'NS (Nameserver)' section. The nameservers listed as (Informational) will be the nameservers the domain needs to use.